A wide variety of human diseases, in their active stages, are characterized by migration of neutrophils across mucosal surfaces. For example, conditions such as bronchitis, cystic fibrosis, bronchial asthma, ulcerative colitis, Crohn's disease and pyelonephritis are all characterized by the transepithelial migration of neutrophils during disease flares. In addition, the histologic finding of neutrophil transepithelial migration is associated with patient symptoms in such conditions. Current evidence suggests that such patient symptomatology is at least partly related to altered epithelial function secondary to neutrophil interactions with the epithelium. With modifications of a model for neutrophil - epithelial interactions, experiments have been performed to identify the neutrophil determinants important in the process of transepithelial migration. It is now clear that the neutrophil beta2 integrin CD11b/CD18 is of major Importance in the transepithelial migration of neutrophils. In addition, we have determined that neutrophil transepithelial migration is modulated by cytokines but remains CD11b/CD18-dependent. The epithelial counterreceptor(s) in this CD11b/CD18 - mediated response appear(s) to be distinct from currently known ligands involved in the process of neutrophil margination and migration across endothelium. Thus, two hypotheses will be tested in this proposal: First, transepithelial migration of neutrophils requires a series of neutrophil- epithelial adhesive interactions which are unique to epithelia (as opposed to endothelia), and second, alterations in neutrophil adherence/transepithelial migration elicited by pretreating epithelia with cytokines such as interferon-gamma are due to altered expression of epithelial ligands for neutrophils. To test such hypotheses, the following specific aims are proposed: 1) To identify surface proteins on intestinal epithelia which serve as ligands for neutrophil binding during transepithelial migration. To approach this aim, I will identify monoclonal antibodies which recognize epitopes that may serve as sites for neutrophil binding. Such antibodies will be used to perform a biochemical and molecular characterization of epithelial ligands. 2) To identify epithelial ligands for CD11b/CD18 and thus reveal surface proteins involved in one specific step in neutrophil binding. To approach this aim, I will use purified human CD11b/CD18 in adhesion and ligand binding assays to identify and characterize epithelial counterreceptor(s). Such assays will also be used to screen interesting antibodies identified in the other specific aims. 3) To identify monoclonal antibodies against interferon- gamma - activated T84 cells which modulate neutrophil - epithelial adhesive interactions under cytokine-activated conditions. Since such neutrophil - epithelial interactions are thought to contribute to disease symptomatology, a better understanding of the molecular basis of these interactions may lead to new therapeutic interventions in the treatment of acute inflammatory diseases of mucosal surfaces.